Generally, with development of mobile technology and an increase in demand for mobile equipments, the demand for secondary batteries is increasing rapidly. In particular, because lithium (ion/polymer) secondary batteries have high energy density and operating voltage and are advantageous in preservation and life characteristics, they are widely used as energy sources for various types of electronic products as well as for many kinds of mobile equipments.
However, such secondary batteries contain various kinds of combustible materials, and thus, they may be swollen at their cases under abnormal conditions such as over-charge, over-voltage, other physical external impact, or when they are left at high temperature, resulting in heat, fire, explosion and so on. That is, secondary batteries have a disadvantage of poor safety. When secondary batteries operate abnormally, one of solutions is to forcibly discharge an electrolyte in the batteries. As another solution, secondary batteries have safety elements such as positive temperature coefficient (PTC) elements, protection circuit modules (PCMs) and so on, to effectively control the abnormal conditions such as over-charge, over-voltage or the like.
In spite of these safety measures, secondary batteries still have a malfunction problem. If there is something wrong with the safety elements, there is a higher probability of malfunction. Therefore, there is an urgent necessity for improved technology to solve the problem.